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Re: [Qemu-block] [Qemu-devel] [PATCH v3 4/5] socket: Add num connections
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH v3 4/5] socket: Add num connections to qio_net_listener_open_sync() |
Date: |
Wed, 4 Sep 2019 14:57:14 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
On Wed, Sep 04, 2019 at 03:19:21PM +0200, Juan Quintela wrote:
> Eric Blake <address@hidden> wrote:
> > On 8/20/19 5:48 AM, Juan Quintela wrote:
> >> Reviewed-by: Daniel P. Berrangé <address@hidden>
> >> Signed-off-by: Juan Quintela <address@hidden>
> >> ---
> >> blockdev-nbd.c | 2 +-
> >> chardev/char-socket.c | 2 +-
> >> include/io/net-listener.h | 2 ++
> >> io/net-listener.c | 3 ++-
> >> migration/socket.c | 2 +-
> >> qemu-nbd.c | 2 +-
> >> ui/vnc.c | 4 ++--
> >> 7 files changed, 10 insertions(+), 7 deletions(-)
> >
> > Just now noticing this one, even though the pull request is already sent...
> >
> >>
> >> diff --git a/blockdev-nbd.c b/blockdev-nbd.c
> >> index 7a71da447f..c621686131 100644
> >> --- a/blockdev-nbd.c
> >> +++ b/blockdev-nbd.c
> >> @@ -101,7 +101,7 @@ void nbd_server_start(SocketAddress *addr, const char
> >> *tls_creds,
> >> qio_net_listener_set_name(nbd_server->listener,
> >> "nbd-listener");
> >>
> >> - if (qio_net_listener_open_sync(nbd_server->listener, addr, errp) < 0)
> >> {
> >> + if (qio_net_listener_open_sync(nbd_server->listener, addr, 1, errp) <
> >> 0) {
> >> goto error;
> >> }
> >
> > Does this interfere with the ability to have more than one client
> > connect to an NBD server during pull-mode incremental backup? Or can
> > you still have multiple simultaneous clients, provided that the server
> > has finished accepting the connection from the first before the second
> > one starts?
>
> It is exactly the same than the old code. Old code always use one. We
> need to have more than one for multifd.
>
> Once told that, if the connections don't start "very" simultaneosly
> (i..e. With multifd we start <num channels> connections in paraller),
> you will never notice that the backlog is one (sie of queue of pending
> connections nowadays).
If incremental backup needs multiple concurrent connections, then
you certainly *do* want to increase this value to something other
than 1, or you will get random failures. As Juan says, this is a
pre-existing problem with NBD though.
Regards,
Daniel
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